In the medical field, the classification of the nebulizer is either mainstream or sidestream. The difference is due to the production of aerosol from the device relative to the main gas flow. For example, by definition with a mainstream nebulizer, main gas flow passes directly through the device and will admix with the carrier gas and aerosol particles. In comparison with a sidestream nebulizer, aerosol with the carrier gas simply drifts out of the device via a conduit and is added to the the main gas flow.
The most predominately prescribed nebulizer is the sidestream due to its simplicity for patient use and low cost.
Presently, in the field of respiratory care several popular versions of the sidestream small volume nebulizer are employed to administer an aerosol of liquid medication.
An example of the basic sidestream nebulizer is U.S. Pat. No. 4,566,452 sets forth a NEBULIZER issued to Farr, a nebulizer having a housing defining a liquid reservoir, a gas nozzle with inlet for introduction of gas to the nozzle. A liquid inlet which is spaced from the gas nozzle for introducing liquid to the gas nozzle as gas flows through the gas orifice. A liquid passage extends along and spaced from a portion of a sidewall which defines the liquid reservoir.
The major disadvantage of the Farr nebulizer is that the device must be held nearly at a vertical position which is necessary to aspirate and aerosolize the bulk of the liquid, and the device will only aspirate the liquid in one particular plane in the horizontal orientation.
Notably, in the United States, a very frequently prescribe small volume sidestream nebulizer is U.S. Pat. No. 4,512,341 issued to Lester which sets forth a NEBULIZER WITH CAPILLARY FEED, the feed to the spray nozzle is through a narrow space between the flat bottom of the liquid reservoir and a flange fixed to the bottom of the spray nozzle, liquid is drawn toward the nozzle by capillary action and aspiration at any orientation of the nebulizer between vertical and horizontal.
Of particular interest, are nebulizer's that will provide an aerosol at different positions or orientation of the device, particularly between the vertical and the horizontal This is necessary to better accommodate the position of the patient, or if the nebulizer is not held substantially vertical, the nebulizer will continue to produce an aerosol and reduce the wastage of medication.
The Lester Patent sets forth a nebulizer to provide aspiration of liquid at any orientation between the vertical an the horizontal. It has been observed that the device will not aspirate the liquid medication continuously in the horizontal orientation, when the volume of liquid has reached critical level for aspiration. The current method employed for the manufacture of plastic components on a large scale, is injection molding. For uniform wall thickness, both the reservoir and cap must have positive parallel draft angles required by the injection molding process to inexpensively manufacture the Lester sidestream nebulizer. The draft angles are typically from 1 to 3 degrees, which are the recommended standards in the industry. The draft angles of the nebulizer with the instilled initial volumes do not dramatically effect the performance of aerosol output when the nebulizer is in the horizontal position. In contrast, draft angles do effect the efficiency of aspiration and is substantially reduced with decreased, small volumes since the liquid is directed away from the described flange. This can result in aspiration stopping altogether, and therefore no production of aerosol. More will be explained later in detail when comparing the prior art nebulizer to the present invention.
Another example of a sidestream nebulizer, is U.S. Pat. No. 4,746,067 issued to Svoboda sets forth a LIQUID ATOMIZING DEVICE AND METHOD, the device may be operated in either a a horizontal position or vertical position by providing a liquid passage to the perimeter of the liquid reservoir by means of an angled liquid conduit formed between a pair of cone members. The Svoboda sidestream nebulizer attempts to correct for the draft angle to maintain the level of liquid in the horizontal position toward an annular opening for aspiration of the liquid. Nevertheless, to construct the liquid container by injection molding methods with the draft angle that will cause the liquid to be directed toward the annular opening, the liquid container is constructed of two parts, an outer cylindrical tapered wall, and a bottom wall consisting of a cone which is attached to the liquid container. Since the nebulizer shown has no removable threaded cap, the nebulizer cannot be disassembled for cleaning and possible reuse. Therefore, the sidestream nebulizer as illustrated is impractical. Also the additional manufacturing costs associated with the assembly of the liquid container. It has been observed, that the Svoboda sidestream nebulizer currently utilized in the medical field has a liquid container constructed of having positive draft angles and a removable threaded cap for disassembly, and thus not having the negative draft angles as depicted. When the Svoboda sidestream nebulizer is in the horizontal position, because of the positive draft angles, the same inherent problem exists as with the Lester sidestream nebulizer.
U.S. Pat. No. 5,008,048 issued to Ryder sets forth a POSITION INSENSITIVE ASPIRATOR, a device for aspirating liquids which is operable from any position or orientation. Includes a hollow housing communicating with a source of carrier gas and a a source of gas under pressure. A nozzle is disposed within the hollow housing through which the pressurized gas is directed to produce a high speed stream of gas. An entrainment member defining an aspiration chamber for liquid is disposed in the housing with the aspiration chamber immediately adjacent to the nozzle outlet in the housing. A multidirectional liquid flow path is defined by the entrainment member edge portions to provide fluid communication regardless of orientation of the device. Albeit this apparatus will achieve the generation of an aerosol regardless of position, it requires more than a few parts, and is preferentially designed for a mainstream configuration which is specifically used in connection with mechanical ventilators.
When considering the dispensing of pulmonary aerosol treatments via a sidestream nebulizer, in most cases it is not essential that a nebulizer function in every orientation.
At present, the prior art sidestream nebulizer will only operate between the vertical and horizontal, however the major benefit of the present invention will aspirate and therefore aerosolize the liquid medication from the vertical to above the horizontal. This will greatly facilitate aerosol therapy for the patient.
Although the forgoing described devices are representative of the prior art, there remains nonetheless a continuing need to improve the performance and capability of aerosol generators, specifically small volume sidestream nebulizers.
It is the object of this invention to provide a small volume sidestream aerosol generator which will be fully functional in the vertical to above the horizontal orientation.
Another object of the invention is to efficiently aspirate the liquid medication to generate an aerosol, at the different positions as described above.
It is the object of the invention to provide the therapeutic range of aerosol particle size from the vertical to above the horizontal.
A further object of the invention is to provide a facile approach concerning the construction and manufacturing of the device. Maintaining or minimizing cost for a sidestream nebulizing apparatus which will generate an aerosol in variable positions